For htmltoword version >= 0.2 An action controller renderer has been defined, so there's no need to declare the mime-type and you can just respond to .docx format. It will look then for views with the extension .docx.erb which will provide the HTML that will be rendered in the Word file.

# On your controller.
respond_to :docx
# filename and word_template are optional. By default it will name the file as your action and use the default template provided by the gem. The use of the .docx in the filename and word_template is optional.
def my_action
# ...
respond_with(@object, filename: 'my_file.docx', word_template: 'my_template.docx')
# Alternatively, if you don't want to create the .docx.erb template you could
respond_with(@object, content: '<html><body>some html</body></html>', filename: 'my_file.docx')
end
def my_action2
# ...
respond_to do |format|
format.docx do
render docx: 'my_view', filename: 'my_file.docx'
# Alternatively, if you don't want to create the .docx.erb template you could
render docx: 'my_file.docx', content: '<html><body>some html</body></html>'
end
end
end